A steam turbine plant is provided with a steam turbine and a piping system having piping through which steam flows. Blowing-out for removing foreign matter in the piping is carried out before the steam turbine plant is started up after the ending of construction for building the steam turbine plant, after the ending of remodeling, and after long-term stoppage. The blowing-out is processing of cleaning the piping by supplying steam to the piping and blowing off foreign matter in the piping by the steam.
In a case where the steam supplied to the piping in the blowing-out is released to the atmosphere (free-blown), a noise problem arises. Further, a problem occurs in that steam which has been changed in color due to rust of the piping is released to the atmosphere. Further, a problem occurs in that a large amount of water is required. In order to deal with these problems, a technique of sending the steam used for blowing-out to a condenser without releasing it to the atmosphere has been devised. PTL 1 discloses an example of a technique related to intra-system blowing in which the steam used for blowing-out is sent to a condenser.